When crowds gather today to read aloud the roll call of those lives lost to 9/11 terrorism, four new names should be added: Christopher Stevens, Sean Smith, Glen Doherty and Tyrone Woods.

These four Americans died a year ago today at the US diplomatic mission in Benghazi, Libya. The violence took place on the 11th anniversary of the deadliest terrorist attack on US soil. That assault on our compound in Benghazi — and the raising of the al Qaeda flag over our embassy in Cairo — ought to remind us that the terrorists who targeted us in 2001 have not given up.

Sometimes, alas, it appears we have forgotten. A year after President Obama’s vow that “justice will be done . . . for this terrible act,” there have been no arrests and no reprisals. While CNN manages to locate and interview suspected mastermind Ahmed Abu Khattala, he’s eluded the reach of the Obama administration. Whatever else it is, this is no way to deter future plots.

On Tuesday, NYPD Commissioner Ray Kelly reminded us that plans for fresh attacks continue unabated. As he put it, “the threat of terrorism is as great, if not greater, today than it was before the World Trade Center was destroyed.”

New York, he added, remains “squarely in the cross hairs.” The point is that if this city hasn’t had to endure another attack, it’s not because the terrorists have given up. Since 9/11, there have been more than a dozen plots to wreak murder and mayhem across New York, all foiled by the NYPD’s counterterrorism efforts.

Today, these threats have expanded to include al Qaeda allies and affiliates throughout Africa and the Middle East. In addition, we remain vulnerable to home-grown terrorists, such as what Americans saw in the Boston bombings by local jihadis.

Which is why, Kelly says, it is so disturbing that the Democratic mayoral candidates have been so reluctant to defend the tactics and strategies that have kept New York safe.

The death that rained down on New Yorkers on that clear September day in 2001 — and on American diplomats in Libya one year ago — reminds us that the War on Terror cannot be called off because one side has grown tired of fighting.

On this 9/11, we mourn the thousands murdered in Lower Manhattan, at the Pentagon, aboard Flight 93 and, more recently, at Benghazi. But we do a disservice to these men and women if we limit 9/11 to memorials and memories, instead of fortifying our resolve to do whatever it takes to defeat the evil men who are as determined as ever to attack our nation and kill our people.